On the basis of the optic principle, it is clear that no matter where the light out of the convex axis comes from, after it passes through the convex, it will be refracted to a point called focus. Usually, the plane composed by all the points located on the positions which can form the clear images is called the focal plane. The objects on the focal plane can form the clear images, and the objects located out of the focal plane form the blurry images.
The general optical inspection instrument, such as the microscope, uses the manual focus method to adjust the distance between the lens and the object or between the lens and the eyes of the observer so as to form the clear image. Observing and manually adjusting together often slows the user's action and results in mistakes easily. However, the critical observations are usually time dependent, which are often missed because of the inaccurate and slow manual adjustment. Therefore, the automatic focusing technique is provided for solving the defects of the manual adjustment.
The distance detecting method is used commonly in the traditional automatic focusing technique which detects the object distance and calculates the image distance corresponding thereto to adjust the system to make it in the accurate focus state. Since the developments of the calculation and the digital image processing theory are maturing, the automatic focusing technique enters a new digital era. There are more and more automatic focusing methods analyzing and calculating the image information based on the image processing theory, and driving the electric motor according to the analyzed and calculated data to adjust the optic system to the precise focus.
Nowadays, the known automatic focusing methods include the steps of the data acquisition and data process, the optimal searching algorithm, the stepping electric motor driving and the zoom tracing, etc. The image data are collected step by step and compared to the preceding one, and the image will be from blurry to clear and become blurred again, so that the search method is like mountain climbing. Using such automatic focusing method, the focus has to be passed by and be re-found by the reverse locating. This iterative computation needs complex calculating processes and thus raises the cost of the hardware thereof. The mountain climbing searching method also delays the time for focusing.
In order to overcome the drawbacks in the prior art, an improved automatic focusing device and method are provided. The particular design in the present invention not only solves the problems described above, but also is easy to be implemented. Thus, the present invention has the utility for the industry.